I. Field of the Invention
The present invention relates to an improved, preferably household gas burner, generally used in the cooking gas appliances.
In the following description it will be referred to as a gas burner provided with both a central body with a peripheral flame crown, and a peripheral body provided with two flame crowns, oriented inwards and outwards, but it will be intended that what is explained may be identically applied, and therefore valid, also to gas burners provided with only a peripheral body, that is without the central flame body.
II. Description of the Related Art
Gas burners are known that are provided with a plurality of flame crowns which assure an homogeneous distribution of the generated thermal power, and therefore provide a uniform heating of the cooking containers/pans placed over the gas burners.
A particularly efficient embodiment of such burners is one which comprises a central body and an outer annular body, the two bodies being basically circular, coaxial and separated to each other by a suitable distance which is horizontally extended, and obviously also shaped as a ring; as such burners are universally used, it is cited, only for documentation, U.S. Pat. No. 6,132,205.
Such burners have been experienced to be particularly efficient as they are able to generate, inside a limited surface, a high specific thermal power, just because they are based on the provision of grouping a certain number, preferably three, concentric flame crowns.
However such burners are not deprived of some drawbacks which limit their use and performances; as a matter of fact, they often show two injectors and two respective Venturi pipes, one feeding the central burner, and the other feeding the outer annular burner.
Moreover it is known that such arrangement allows the delivery thermal powers which can hardly exceed 4-4.5 kW.
It is also known that a Venturi pipe becomes more efficient when its length is proportional to the Venturi throat diameter, and it is also well known that the latter dimension determines the burner thermal power. As a consequence, to delivery large power, it is needed to provide long-neck Venturi pipes, able of sucking more air and to closely mix the air with the gas.
As the central burner size is unavoidably limited, it would be in any case not able of providing a high thermal power; therefore the respective gas injector and respective Venturi pipe may be limited in their extension, and so the injector and the respective Venturi pipe may normally be oriented vertical, without causing a remarkable penalization.
As a matter of fact, it is here reminded that the height of the cooking gas hobs, specifically for household use, must be comprised within definite limits, usually 30 to 40 mm.; therefore a limited height of the Venturi pipe for the central burner turns to be also compatible with such height limit, and so the vertical orientation of the Venturi pipe which is shorter for the central burner becomes compatible both with its limited thermal power that can be delivered, and with its vertical height that can be admitted.
The case of the outer annular burner is different; in such a case, it is needed to deliver high thermal power, and this need hinders the bounds of a properly prolonged and vertically positioned Venturi pipe.
In order to overcome such a drawback it is known, for instance from WO 2004/044490 A1, U.S. Pat. No. 6,132,205, WO 2005/073630 A1, WO 0712766 A1, WO 2005/078342 A1 to split the gas flow into a plurality of usually two or three separate and distinct injectors, and respective Venturi pipes which are obviously distinct as well.
As a matter of fact, it is also known to split the gas flowing means (injectors and Venturi pipes) into a plurality of conduits showing a lower delivery and so with a lower single thermal power, but also with shorter lengths, easily allowing to reach and also to overcome the power of a single conduit (injector and Venturi pipe) having the same gas delivery as the sum of the gas deliveries of the previous conduits.
However even such conditions do not properly offer the best compromise between:                the desired minimum vertical size of said gas conduits,        the burner geometric shape and size, which appear to be over-sized with respect to the cooking pots/containers,        and the maximization of the overall deliverable power,        
as the conduits (injectors and related Venturi pipes) are in any case vertical, and the fact that they are vertical restricts their length, and therefore the deliverable thermal power.
Moreover, as the pipes must be lodged inside the burner, it turns that, when their number increases, the burner becomes more and more cumbersome.
This circumstance causes a performance decrease, as the heat is being transferred from the burner to the sides of the cooking pot, instead of on its bottom; as a consequence the heat transfer is obviously hindered, and the gas consumption and cooking time are experienced.
WO 07012766A1 and WO 2005/078342 respectively show three and two conduits which are remarkably inclined on the horizon, but the conduits (injectors and Venturi pipes) also originate on the burner central axis, and therefore they stretch radially for only an extension which is similar to about the burner radius, within limits their length, and consequently the deliverable thermal power; moreover the injectors positioning in the burner centre, i.e. far away from the burner side edge, obstacles the primary (A) and secondary (B) air inlets, due to the over-heating and of the consequent gas rarefaction.
In order to overcome such a drawback, from EP 1120603 B a kind of gas burner of the generally described kind is known, with three coaxial flame crowns generated by burners split into a central body and a outer annular body, wherein an injector and a respective Venturi pipe are arranged to feed the outer annular body and which are placed both in horizontal and for the whole extension of the burner lower diameter.
Such a solution apparently overcomes the bound due to the limited extension in the length of the gas conduit, as it makes use of the maximum available extension; however in this case too it is not possible to deliver the maximum possible power as the gas conduit is only one, being that there is not any splitting in the gas conduits implemented; as a consequence there is an apparent discrepancy between the horizontal arrangement of the gas conduit, which prolonging the Venturi pipe, increases its power, and the singleness (no splitting) of the injector and of the Venturi pipe, which prevents the full exploitation of the available room to maximize the theoretically installable thermal power.
Moreover like solutions more precisely suffer primary air rarefaction, caused by the heating induced by the working burner itself; this can be demonstrated by the presence of tips of yellow flames after about ten minutes from the burner ignition.
Furthermore, the fact of placing the Venturi pipe in the centre of the lower burner portion apparently hinders, creating further functional and constructive problems, the injector assembly and the lodging of the related vertical Venturi pipe which feeds the central body and which evidently has to pass through the burner axis, which in the presently cited patent is instead taken by the horizontal Venturi pipe.